The Dipneusti and Crossopterygii 315 



tensive study has been made of the rocks at Southeram, 

 Maidstone, Hamsey, Steyning, Dover, and other localities 

 of South England, as well as similar regions on the conti- 

 nent, the writer would withhold opinion on this suggested 

 lone marine derivative of the otherwise freshwater coela- 

 canth series. 



The two surviving genera of this great group, namely 

 Poly pt ems and Calamichthys that occur over a large area 

 of the river and lake systems of Central Africa, seem to 

 be ancient and highly modified derivatives of still older 

 genera. These must, long since, have passed southward 

 into the Gondwana continent. It is not unlikely, however, 

 that once the Cretaceous and Tertiary deposits of that 

 ancient land-mass are better known, connecting links be- 

 tween them and more remote ancestors of Jurassic or Trias- 

 sic age may be secured. 



